Things to look for when reviewing MIDS calculator files and submissions
This site is currently undergoing revision. For more information, open this link.
This page is being developed
This page is being developed
Many people have expressed interest in knowing what to look for when reviewing MIDS calculator files, including submissions from projects where the calculator was used. This page provides a summary of some things to look for. The page will continue to evolve since we get questions about the calculator and will incorporate those communications into this page. The page includes information for entire sites and individual BMPs.
Permeable pavement
- The calculator limits the ratio of impervious acres to permeable pavement acres to 5:1, but the manual recommends a 2:1 ratio. Since this is a very effective infiltration BMP, it can be used to meet a performance goal by routing large impermeable acreages to the BMP. BMP ratios greater than 2:1 or 3:1 should be viewed with caution.
- Permeable pavement is often used in combination with other BMPs and can therefore easily result in double counting. Water infiltrated through permeable pavement is considered to infiltrate into underlying soil. impermeable acres for this type of practice cannot be applied to other BMPs. For example, impervious acres routed to permeable pavement that infiltrates into a tree trench system should be applied to the tree trench system and not the permeable pavement.
- If the permeable pavement BMP is not meeting or barely meeting the performance goal, see if the subsoil is compacted. If the answer to this question is "No", determine if this is correct, since many if not most permeable pavement practices will require compaction.